1. Field of the Invention
The present invention relates to a method for manufacturing a toner, and to a toner.
2. Description of the Related Art
An electrophotographic image forming apparatus comprises an image forming process mechanism including a photoreceptor; a charging section for charging a surface of the photoreceptor; an exposure section for irradiating the surface of the photoreceptor being charged with signal light to form thereon an electrostatic latent image corresponding to image information; a developing section for supplying a toner contained in a developer to the electrostatic latent image formed on the surface of the photoreceptor to form thereon a toner image; a transfer section provided with a transfer roller for transferring the toner image formed on the surface of the photoreceptor to a recording medium; a fixing section provided with a fixing roller for fixing the toner image onto the recording medium; and a cleaning section for cleaning the surface of the photoreceptor after the toner image has been transferred. In the electrophotographic image forming apparatus, the electrostatic latent image is developed using a one-component developer containing a toner as a developer, or a two-component developer containing a toner and a carrier as developers to form an image.
The electrophotographic image forming apparatus can form an image having fine image quality at high speeds and low costs, thereby being utilized for copying machines, printers, facsimiles and the like, along with remarkable popularization thereof in recent years. Simultaneously, the image forming apparatus has encountered more demanding requirements. Among such requirements, requirements to fulfill high-definition, high-resolution, high-quality stability, and an increase in an image forming speed and the like in an image formed by the image forming apparatus have attracted particular attentions. To achieve these requirements, it is essential to consider a two-way approach from an image forming step point of view and a developer point of view. In respect with an approach to high-definition and high-resolution in the image, as long as the developer concerned, one of the problems to be solved is to reduce a diameter of toner particles based on the perspective that it is important to precisely reproduce the electrostatic latent image. The toner particles are typically resin particles in which a wax as a colorant and a releasing agent are dispersed in binder resin as a matrix, resulting that it is difficult to reduce a particle diameter of the wax dispersed in the binder resin by typical methods for manufacturing toner particles having a reduced diameter. Accordingly, there is a problem that the wax bleeds out as time advances from the toner particles having a reduced diameter that have been manufactured onto a surface of the toner particles, thus causing toner filming on the surface of the photoreceptor. Moreover, a great amount of wax bleeds out onto a surface of the toner particles and thereby the wax is melt to have viscosity especially at a high temperature. As a result, an offset phenomenon that the toner is adhered to the transfer roller and the fixing roller and the like without being transferred or fixed to a recording medium, may frequently occur.
As a method for reducing the particle diameter of the wax, for example, in Japanese Unexamined Patent Publication JP-A 6-161153 (1994) there has been proposed a method for manufacturing a toner including a mixing step in which at least 100 parts by weight of thermoplastic resin and 1 to 7 parts by weight of wax are mixed, a melt-kneading step in which a mixture obtained in the mixing step is melt-kneaded and its melt-kneading temperature is in a range of (Tm−20) to (Tm+20)° C. (Tm: a melting temperature of the thermoplastic resin) and a melt-kneaded product after the melt-kneading step has a temperature of (Tm+35)° C. or less, and a pulverizing-classifying step in which the melt-kneaded product obtained in the melt-kneading step is cooled, pulverized, and classified. Additionally, in a method for manufacturing a toner in which a mixture of toner raw materials is melt-kneaded, and a resulting melt-kneaded material is cooled, pulverized and classified, there has been proposed a method for manufacturing a toner, in which the mixture of the toner raw materials is melt-kneaded using an extruder/kneader configured so that a slide-shaped discharging part inclining downward is coupled on an outlet of a cylinder part internally having a kneading-conveying member for kneading and conveying the mixture of the toner raw materials, as disclosed in Japanese Unexamined Patent Publication JP-A 9-277348 (1997), for example. These methods for manufacturing a toner are intended to prevent occurrence of the toner filming on the photoreceptor due to bleeding out of the wax, the offset phenomenon and the like by reducing a particle diameter of the wax contained in the toner particles. However, these methods, which are basically a melt-kneading method that is conventionally known, fail to contribute to sufficient particle diameter reduction of the toner itself, even though the particle diameter of the wax may have been successfully reduced. Therefore, the toner particles obtained are not sufficiently satisfactory in image reproducibility, particularly, in high-definition and high-resolution.
Meanwhile, in International Publication WO03/059497, for example, there has been proposed an emulsifying/dispersing apparatus including an emulsifying/dispersing section for emulsifying and dispersing emulsifying materials into liquid as a matrix by a shear force, a leading passage for supplying the emulsified liquid under pressure that is obtained by the emulsifying/dispersing section to a multistage depressurizing section, a heat exchanging section provided on the leading passage, and the multistage depressurizing section for depressurizing the emulsified liquid supplied from the leading passage down to such a level that the emulsified liquid discharged into the atmosphere causes no bubbling, and then discharging the emulsified liquid. The emulsifying/dispersing apparatus disperses the emulsifying materials into the liquid under pressure to prepare the emulsified liquid in which the emulsifying materials are uniformly dispersed, and then depressurizes in a stepwise manner the emulsified liquid finally down to such a level that the emulsified liquid causes no bubbling to prevent the particles of the emulsifying materials dispersed in the emulsified liquid from coarsening, thus obtaining the objective emulsified liquid in which the particles of the emulsifying materials having a uniform diameter is dispersed. By using the emulsifying/dispersing apparatus provided with the multistage depressurizing section, a high share force can be applied in the emulsifying/dispersing section to readily produce emulsion composed of water and oil, and the like, for example. However, when it is merely intended to obtain the toner particles using this apparatus, it is difficult to control the particle diameter, resulting that the desired toner particles having a reduced diameter cannot be obtained. WO03/059497 has no disclosure about application of this emulsifying/dispersing apparatus to a manufacturing method for toner particles. Moreover, WO03/059497 has no suggestion that when the emulsifying/dispersing apparatus disclosed in WO03/059497 is applied for a method for toner particles, not only is toner particles having a reduced diameter obtained, but a toner in which wax having a more reduced diameter than the reduced diameter of the toner particles is uniformly dispersed in the toner particles is obtained.